Well, I've deadened and nearly completely sealed my doors. I also made some 3/4" MDF baffles for this set of comps. The deadening + sealing + baffles do make a big difference, so it was definitely worth the time. I flush mounted the tweeters on the kicks off-axis facing the center console.
I just bought a DMM, but I'm not sure how to use it and I'm pretty tired right now anyway. I've got the Alpine MRP-F300 for my comps, bridged down to two channels. I'm really not sure how much these speakers are actually seeing in power (hopefully around 100w RMS with the passive crossover), but I do think they can handle a smidge more. Gotta set the gains tomorrow, I suppose.
Initially, I wasn't too impressed by what I heard. The doors were pretty much stock at the time, though. I've changed some settings, enabling the +2 db for the tweeter on the crossover. On my Pioneer DEH-3600, I've got the HPF at 80hz. I've set the mids at 1K to -4, because IMO they can get quite harsh with hard rock and such. Everything else is flat, no loudness, bass boost, etc. It seems like a drastic drop for the mids on the EQ to me, but eh, it sounds good to me. I'm listening to music on my 30 GB Zune on the flat EQ setting. They were mostly ripped at 192 kbps and they sound pretty good.
For $70 shipped, they're pretty nice. Just gotta do a proper install and a bit of EQ to get the most out of them, like others have suggested.
Now I've gotta try and make a proper enclosure for my sub...